Add native block-editor support

• Add wp-scripts for build
• Enqueue script, excluding it from widget block editor
• Localize script with configurable/filterable options
• Localize script with titles for post types to match current functionality
• Register meta and set sanitization callbacks
• Allow meta to be accessed via endpoint
• Create sidebar plugin to show the two fields used by the plugin

.gitignore

@@ -5,6 +5,7 @@ Thumbs.db
 wp-cli.local.yml
 node_modules/
 .idea/
+*.map
 *.sql
 *.tar.gz
 *.zip